Injection molding provides a convenient way for manufacturing various articles from thermoplastic resins, particularly objects of a relatively intricate nature. In order to injection mold articles in an economic manner, it is important to minimize the adhesion of the molded part to the mold surface through the use of an effective release agent. It is additionally advantageous that the release agent be incorporated in the material to be demolded. However, such an internal agent must be compatible with the resin; that is, its use should not lead to any significant loss of the other physical properties such as transparency, color and melt stability as measured by the usual characteristics of the resin under normal conditions and heat treatments.
It is well known to one skilled in the art that a particular internal release agent which is satisfactory for one type of thermoplastic resin may not be effective with another type. This is not surprising in view of the diversity of the chemical compositions of different thermoplastics. Thus, there is a continuing need to discover release agents that do not detract from the properties of virgin resin and yet provide efficient and reliably reproducible release at low concentrations.
Mineral oils are one type of mold release agents as described in Nos. K53,22556; K79,16559; K72,41093; K80,84353 and GB Pat. No. 2,077,742. Mineral oils are naturally occuring complex mixtures of hydrocarbons that are obtained from petroleum. U.S. Pat. No. 4,626,566 to Miller et al. describes and claims aromatic carbonate polymer compositions in admixture with a hydrogenated alpha olefin oligomer fluid as mold release agent.